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1. General Principles & Basic Science MCQs

Practice Set 22 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 421

Topic: Infection, Pharmacology & VTE

Which of the following is NOT one of the classic Kocher criteria used to differentiate septic arthritis of the hip from transient synovitis in children?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. Temperature > 38.5°C (101.3°F)
. Serum C-reactive protein (CRP) > 2.0 mg/dL
. Serum white blood cell (WBC) count > 12,000 cells/mm3

Correct Answer & Explanation

. Serum C-reactive protein (CRP) > 2.0 mg/dL

Explanation

The classic Kocher criteria include non-weight-bearing, ESR >40, fever >38.5°C, and WBC >12,000. While CRP >2.0 mg/dL was later identified by Caird et al. as an excellent independent predictor, it is not one of the original four Kocher criteria.

Question 422

Topic: Infection, Pharmacology & VTE
A 2-year-old girl presents with a warm, swollen knee and refusal to walk. Aspiration yields purulent synovial fluid, but standard agar cultures remain sterile at 48 hours. What is the optimal method for isolating the most likely causative organism in this age group?
. Prolonged incubation on MacConkey agar for 14 days
. Inoculation of the synovial fluid into aerobic BACTEC blood culture vials
. Acid-fast bacilli (AFB) staining and Lowenstein-Jensen culture
. Viral culture of the synovial fluid
. Direct immunofluorescence assay for Borrelia burgdorferi

Correct Answer & Explanation

. Inoculation of the synovial fluid into aerobic BACTEC blood culture vials

Explanation

Kingella kingae is a fastidious organism and a leading cause of septic arthritis in children aged 6 months to 4 years. Its isolation is significantly improved by inoculating synovial fluid directly into aerobic blood culture vials or by using PCR.

Question 423

Topic: Infection, Pharmacology & VTE

A 9-year-old boy presents with severe right thigh pain, fever, and inability to bear weight.

MRI reveals a large subperiosteal abscess. If blood cultures grow Community-Acquired MRSA (CA-MRSA), which of the following complication screening protocols is highly recommended?

. Routine serial echocardiograms for 6 weeks
. Venous duplex ultrasound of the affected extremity
. Daily fundoscopic examinations
. Renal ultrasound for glomerulonephritis
. Lumbar puncture to rule out meningitis

Correct Answer & Explanation

. Venous duplex ultrasound of the affected extremity

Explanation

CA-MRSA osteomyelitis in children is strongly associated with deep vein thrombosis (DVT) and septic pulmonary emboli. Routine screening with venous duplex ultrasound of the affected limb is recommended due to the high incidence of associated DVT.

Question 424

Topic: Infection, Pharmacology & VTE

A 10-year-old boy develops osteomyelitis of the calcaneus after stepping on a rusty nail that penetrated his rubber-soled sneaker. Which organism must be specifically covered by empiric antibiotic therapy?

. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Streptococcus pyogenes
. Clostridium perfringens
. Bacteroides fragilis

Correct Answer & Explanation

. Pseudomonas aeruginosa

Explanation

Puncture wounds through rubber-soled shoes have a high association with Pseudomonas aeruginosa osteomyelitis. Empiric therapy must include anti-pseudomonal coverage, and surgical debridement is often required.

Question 425

Topic: Infection, Pharmacology & VTE

A 6-year-old girl with sickle cell disease presents with high fever, severe right arm pain, and localized swelling over the humerus. Which of the following is the most appropriate empiric antibiotic regimen while awaiting cultures?

. Intravenous penicillin G alone
. Intravenous cefazolin alone
. Intravenous third-generation cephalosporin and vancomycin
. Oral ciprofloxacin and clindamycin
. Intravenous ampicillin and gentamicin

Correct Answer & Explanation

. Intravenous third-generation cephalosporin and vancomycin

Explanation

Children with sickle cell disease are at high risk for osteomyelitis caused by both Salmonella species and Staphylococcus aureus. Empiric coverage should include a third-generation cephalosporin (for Salmonella) and vancomycin or clindamycin (for MRSA).

Question 426

Topic: 1. General Principles & Basic Science

A 9-year-old girl has a 6-month history of recurrent multifocal bone pain. Radiographs show lytic lesions with sclerotic borders in her clavicle and distal femur. Multiple bone biopsies have shown only sterile acute and chronic inflammation. Which of the following is the recommended initial management?

. Six weeks of intravenous vancomycin
. Surgical curettage and bone grafting
. Administration of nonsteroidal anti-inflammatory drugs (NSAIDs)
. Radiation therapy
. Prolonged immobilization in a cast

Correct Answer & Explanation

. Administration of nonsteroidal anti-inflammatory drugs (NSAIDs)

Explanation

The clinical picture describes Chronic Recurrent Multifocal Osteomyelitis (CRMO), an autoinflammatory disorder. The first-line treatment is nonsteroidal anti-inflammatory drugs (NSAIDs), followed by bisphosphonates or biologics for refractory cases.

Question 427

Topic: Infection, Pharmacology & VTE

In children, the blood supply to the epiphysis directly communicates with metaphyseal vessels across the physis. This transphyseal vascular connection, which allows metaphyseal osteomyelitis to easily spread into the joint, typically obliterates by what age?

. 6 months
. 18 months
. 3 years
. 5 years
. 7 years

Correct Answer & Explanation

. 18 months

Explanation

Transphyseal vessels exist in children up to approximately 18 months of age. After this age, the physis acts as a barrier to the spread of infection, making concurrent osteomyelitis and septic arthritis less common until the physis closes in late adolescence.

Question 428

Topic: Infection, Pharmacology & VTE

The Panton-Valentine leukocidin (PVL) toxin is a major virulence factor in Community-Acquired MRSA. What is its primary pathogenic mechanism in orthopedic infections?

. It binds to the Fc portion of IgG to prevent opsonization
. It creates pores in the leukocyte cell membrane, leading to cell lysis and severe tissue necrosis
. It degrades hyaluronic acid in the extracellular matrix
. It prevents the binding of beta-lactam antibiotics to penicillin-binding proteins
. It forms a protective biofilm around the bacterial colony

Correct Answer & Explanation

. It creates pores in the leukocyte cell membrane, leading to cell lysis and severe tissue necrosis

Explanation

The PVL toxin is a cytotoxin that forms pores in the membranes of leukocytes (neutrophils), causing rapid cell lysis. This massive leukocyte destruction releases damaging enzymes, causing the severe, necrotic inflammation typical of CA-MRSA infections.

Question 429

Topic: 1. General Principles & Basic Science

A 16-year-old female presents with acute knee swelling, migratory polyarthralgia, and painless vesiculopustular skin lesions on her extremities. Gram stain of the synovial fluid is likely to reveal which of the following?

. Gram-positive cocci in clusters
. Gram-positive cocci in chains
. Gram-negative intracellular diplococci
. Gram-negative bacilli
. Acid-fast bacilli

Correct Answer & Explanation

. Gram-negative intracellular diplococci

Explanation

The clinical presentation is classic for disseminated gonococcal infection (DGI), caused by Neisseria gonorrhoeae. This organism is a Gram-negative intracellular diplococcus.

Question 430

Topic: 1. General Principles & Basic Science

A 13-year-old boy complains of dull, aching pain in his distal tibia, which frequently wakes him at night and is relieved by ibuprofen. MRI demonstrates a metaphyseal intraosseous abscess with a hyperintense inner ring on T1-weighted imaging. What is this MRI finding called?

. The penumbra sign
. The double-line sign
. The reverse halo sign
. The salt-and-pepper sign
. The string sign

Correct Answer & Explanation

. The penumbra sign

Explanation

The "penumbra sign" is characteristic of a Brodie's abscess on MRI. It consists of a T1-hyperintense rim of granulation tissue lining the abscess cavity, separating it from the surrounding sclerotic bone.

Question 431

Topic: Infection, Pharmacology & VTE

A 14-year-old is prescribed a prolonged 6-week course of oral linezolid for a complex MRSA osteomyelitis. Which of the following complications requires routine monitoring during the duration of therapy?

. Ototoxicity and hearing loss
. Nephrotoxicity and acute kidney injury
. Thrombocytopenia and myelosuppression
. Red man syndrome
. Tendon rupture

Correct Answer & Explanation

. Thrombocytopenia and myelosuppression

Explanation

Prolonged use of linezolid (>2 weeks) is associated with reversible myelosuppression, most commonly manifesting as thrombocytopenia. Regular complete blood counts (CBC) must be monitored; peripheral and optic neuropathy are also risks.

Question 432

Topic: Infection, Pharmacology & VTE

A 7-year-old boy from Massachusetts presents with a swollen, warm right knee, but no fever or signs of systemic toxicity. He has full range of motion of the knee without severe pain. What is the most appropriate initial diagnostic test for the suspected etiology?

. Synovial fluid acid-fast smear
. Serum enzyme-linked immunosorbent assay (ELISA) for Borrelia burgdorferi
. Polymerase chain reaction (PCR) for Neisseria gonorrhoeae
. Blood cultures for Staphylococcus aureus
. Serum antinuclear antibody (ANA) testing

Correct Answer & Explanation

. Serum enzyme-linked immunosorbent assay (ELISA) for Borrelia burgdorferi

Explanation

The child likely has Lyme arthritis, characterized by large joint effusions (especially the knee) without the extreme pain or systemic toxicity seen in bacterial septic arthritis. The initial test is a screening ELISA, followed by a confirmatory Western blot if positive.

Question 433

Topic: Infection, Pharmacology & VTE

A 10-year-old boy presents with fever, limp, and severe tenderness over his mid-thigh. MRI reveals a large, rim-enhancing fluid collection within the vastus intermedius, but the adjacent femoral marrow shows normal signal intensity. What is the most common causative organism for this condition in temperate climates?

. Streptococcus pneumoniae
. Staphylococcus aureus
. Escherichia coli
. Mycobacterium tuberculosis
. Clostridium septicum

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

The diagnosis is primary pyomyositis (abscess in the muscle without underlying osteomyelitis). Even in temperate climates, Staphylococcus aureus is the most common causative organism for primary pyomyositis.

Question 434

Topic: 1. General Principles & Basic Science

A 9-year-old girl presents with vague buttock pain, fever, and a noticeable limp. Hip range of motion is full but painful at the extremes, and the FABER test is markedly positive. Plain radiographs are normal. What is the most appropriate next step in management?

. Diagnostic aspiration of the hip joint
. Magnetic resonance imaging (MRI) of the pelvis
. Bone densitometry (DEXA scan)
. Reassurance and observation for 2 weeks
. Corticosteroid injection of the sacroiliac joint

Correct Answer & Explanation

. Magnetic resonance imaging (MRI) of the pelvis

Explanation

The clinical picture suggests pelvic osteomyelitis or sacroiliac joint infection, which is notoriously difficult to diagnose clinically and typically shows normal early X-rays. MRI of the pelvis is the gold standard for definitive diagnosis.

Question 435

Topic: Infection, Pharmacology & VTE

Rapid destruction of articular cartilage in bacterial septic arthritis of the hip is primarily caused by which of the following mechanisms?

. Direct mechanical abrasion from intra-articular bacterial colonies
. Proteolytic enzymes and matrix metalloproteinases released from synovial cells and neutrophils
. Ischemic necrosis of the subchondral bone secondary to elevated joint pressures
. Osteoclastic resorption triggered by circulating parathyroid hormone
. Crystallization of bacterial byproducts within the cartilage matrix

Correct Answer & Explanation

. Proteolytic enzymes and matrix metalloproteinases released from synovial cells and neutrophils

Explanation

Cartilage destruction in septic arthritis is largely mediated by the host's immune response. Neutrophils and hyperplastic synovial cells release massive amounts of proteolytic enzymes, lysozymes, and matrix metalloproteinases that rapidly degrade glycosaminoglycans and collagen.

Question 436

Topic: Infection, Pharmacology & VTE

When interpreting culture susceptibilities for a methicillin-resistant Staphylococcus aureus (MRSA) isolate from a pediatric osteomyelitis case, a positive "D-zone test" indicates which of the following?

. Inherent resistance to vancomycin
. Inducible resistance to clindamycin
. Susceptibility to daptomycin
. Presence of the Panton-Valentine leukocidin (PVL) toxin
. Beta-lactamase overproduction

Correct Answer & Explanation

. Inducible resistance to clindamycin

Explanation

The D-zone test identifies isolates that appear susceptible to clindamycin on standard testing but possess inducible macrolide-lincosamide-streptogramin B (iMLS_B) resistance. If the test is positive, clindamycin should not be used for treatment due to the risk of clinical failure.

Question 437

Topic: Infection, Pharmacology & VTE

Community-acquired MRSA is characterized by the presence of Panton-Valentine leukocidin (PVL). What is the primary mechanism of action of this virulence factor?

. Inhibition of bacterial cell wall synthesis
. Binding directly to MHC class II forming a superantigen
. Creating pores in the membranes of leukocytes causing cell lysis
. Inhibiting phagosomal maturation in macrophages
. Cleaving host IgA antibodies

Correct Answer & Explanation

. Creating pores in the membranes of leukocytes causing cell lysis

Explanation

PVL is a cytotoxin that creates pores in leukocyte membranes, leading to their destruction and increased tissue necrosis. This virulence factor is strongly associated with the aggressive soft tissue infections and severe osteomyelitis seen in CA-MRSA.

Question 438

Topic: Infection, Pharmacology & VTE
Community-acquired MRSA (CA-MRSA) typically contains which of the following staphylococcal cassette chromosome mec (SCCmec) elements compared to hospital-acquired MRSA (HA-MRSA)?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type IV

Explanation

CA-MRSA is most commonly associated with SCCmec type IV. This element is smaller, more mobile, and typically does not carry the multi-drug resistance genes found in HA-MRSA (Types I, II, and III).

Question 439

Topic: Infection, Pharmacology & VTE

A 9-year-old boy with severe community-acquired MRSA (CA-MRSA) tibial osteomyelitis experiences persistent tachycardia and swelling in the affected limb despite adequate surgical debridement and IV vancomycin. What is the most likely associated complication?

. Fungal superinfection
. Deep venous thrombosis
. Compartment syndrome
. Antibiotic-induced nephritis
. Pathologic fracture

Correct Answer & Explanation

. Deep venous thrombosis

Explanation

Severe CA-MRSA osteomyelitis in children is highly associated with adjacent deep venous thrombosis (DVT) and septic pulmonary emboli. Prompt venous duplex imaging is indicated when limb swelling or respiratory symptoms arise.

Question 440

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with an acute monoarticular knee effusion, low-grade fever, and refusal to bear weight. Aspiration yields purulent fluid, but standard agar plates show no growth at 48 hours. Which of the following is the most appropriate method to isolate the most likely causative organism?
. Polymerase chain reaction for Borrelia burgdorferi
. Inoculation of fluid into blood culture vials (BACTEC)
. Acid-fast bacillus (AFB) staining
. Culture on Thayer-Martin agar
. Sabouraud dextrose agar culture

Correct Answer & Explanation

. Inoculation of fluid into blood culture vials (BACTEC)

Explanation

Kingella kingae is a fastidious Gram-negative organism that is a leading cause of septic arthritis in children under 4. It requires inoculation into aerobic blood culture vials (BACTEC) to enhance recovery rates.

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